1. Field of the Invention
This invention relates to an auxiliary power steering for motor vehicles with an electromagnetically activated proportional valve.
2. Description of the Prior Art
A generic auxiliary power steering is known according to EP 01 42 988 B1. Here, a delta voltage is generated by a triangular generator and is compared to a required voltage of a servo amplifier. A delta voltage with a constant frequency, predetermined by the triangular generator, develops at the output of the comparator. The pulse length is generated in proportion to the required voltage value. This results in a constant energizing frequency for the valve. Such valves frequently produce a whistling sound that is noticed in the vehicle and that is felt to be very annoying.